Einstein’s Theory of Gravitational Redshift Has Just Been Proven On a Supermassive Scale

Thursday, 26 July 2018 - 1:40PM
Astrophysics
Astronomy
Black Holes
No
Thursday, 26 July 2018 - 1:40PM
Einstein’s Theory of Gravitational Redshift Has Just Been Proven On a Supermassive Scale
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Image Credit: Edited from Pixabay
One aspect of Einstein's theory of general relativity has just been proven on an unheard-of supermassive scale at the center of the Milky Way Galaxy. Previous observations "only" involved neutron stars and other celestial objects weighing no more than a couple dozen solar masses… This one clocks in at four million.

A key component of Einstein's theory of general relativity is the "gravitational redshift" phenomenon, whereby light is distorted and stretched as it struggles to escape a larger gravitational force (like a black hole). Think of light as a coiled spring: at one end the coils are densely packed, representing violet. When the gravity of a black hole stretches this spring, the coils – or wavelengths – get longer, shifting into red. This phenomenon has been predicted, but never observed – until now.

For twenty years, astronomers have monitored a star named S2 circling the massive black hole Sagittarius A* that lurks in the center of our galaxy. This star's orbit is an extreme ellipse – taking it closer to the black hole than any other known object in the universe once every sixteen years.

The last time this happened our equipment wasn't advanced enough to measure it. When S2 made another approach in May, astronomers scrambled to capitalize on the opportunity. "We were always running up against the deadline. It was extremely stressful for the team," says Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics.

As S2 swooped into its final approach on the supermassive black hole, teams of astronomers from Europe to Hawaii trained their telescopes on the heart of our galaxy and held their breath. Would the theory of relativity hold up on such a massive scale?



Short answer: Yes. Sagittarius A* latched on to the star like a stage-five clinger, warping its radial velocity by 200 kilometers per second and stretching the light wavelengths it emitted. These results align with Einstein's theory and can't be explained by Newtonian physics alone.

"In sport, you would say it was 1-0 for Einstein," said Frank Eisenhauer of the Max Planck Institute.

Astronomers hope to test other aspects of general relativity against these results – and they're not necessarily hoping Einstein will pass.

"What we hope is at some point we will see something in the galactic centre that we can't explain with Einstein's theory…Because then we could go back to the drawing board and come up with something better," claims Odele Straub of the Paris Observatory.

It's a bold move, Cotton.



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